Heater cord



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HEATER CORD Filed March lO, 1947 lll m 00) m X' lll Dmon-Resin M C w d C Vim-Resin Asbesios Patented Nov. 28, 1950 HEATER CORD Joseph B. Whyland, Hamden, Conn., assignor to The Whitney Blake Company, Hamden, Conn., a corporation of Connecticut Application March 10, 1947, Serial No. 733,675

4 Claims. 1

The present invention relates in general to electrical conductors and more especially to an improved heater cord for use on electric irons,

electric toasters, and similar appliances.

The life of a heater cord is designated by the Underwriters Laboratory specifications as the number of cycles or exings the cord will withstand on the Underwriters Laboratory Standard heater-cord testing machine, and within prescribed latitudes, the cord may be either 3,000 cycle or 10,000 cycle cord. Despite these life-cycle standards, however, heater cords in common use today do not have life expectancies, in general, which even approximate the life of the appliance to which they are attached or with which they are used.

An object of the present invention is to provide a superior heater cord designed and constructed to be a permanent installation of the appliance with which it is associated.

A still further object of the invention is to provide a superior heater cord which meets the Underwriters Laboratory specications .and which has a life expectancy approximating the useful life of the appliance to which it is attached.

A still further object of the invention is to provide a superior heater cord having a high cycleor flex-life and improved resistance to abrasion.

With the above and other objects in view, as will appear to those skilled in the art from the present disclosure, this invention includes all features in the said disclosure which are novel over the prior art.

In the accompanying drawings, in which certain modes of -carrying out the present invention are shown for illustrative purposes:

Fig. 1 is a broken side elevation of the improved heater cord of this invention, the outer braid, asbestos roving, and insulation being peeled back to show the construction of the cord; and

Fig. 2 is an enlarged sectional end elevation of the cord on line 2-2 of Fig. 1.

The construction of heater cords is prescribed by the Underwriters Laboratory specifications which permit, in general, three types of heater cord, namely, a cord comprising a pair of insulated conductors each wound about with asbestos roving and twisted together to form a single cord over which a cotton braid is applied. This type of cord is designated by the letters HPD. A second form of heater cord specified by the Underwriters Laboratory and designated by the letters HC diiers from the aforementioned cord in having braids applied to each asbestos-wound insulated conductor, the braid-covered conductors being subsequently twisted together. A third type of heater cord designated by the Underwriters Laboratory as type HSJ comprises either one of the other two types mentioned above but provided with a rubber jacket substantially 0.0312 inch thick.

The specifications for the insulated conductors are the same for each of these three types of cord, the requirements being the use of soft copper strands with a minimum diameter of 0.005 inch and a maximum diameter of 0.0126 inch, the smaller strands being used for cords of longer ex-life. Other specications for the insulated conductors are a maximum lay of two inches for the twisted strands, a separator comprising cotton, paper or cellophane between the copper strands and the insulation, and insulation comprising vulcanized or unvulcanized rubber or a plastic material with a minimum wall thickness of 0.0156 inch.

It will be evident that in view of the specications of the Underwriters Laboratory and other factors such as the optimum size and weight of the heater cord and its external appearance, that the problem of producing a heater cord having superior ex endurance and abrasion resistance is not simply a matter of increasing the number of strands of wire and decreasing the diameter of the individual strands.

The present invention relates to the development of a superior heater cord which will meet not only the Underwriters Laboratory specifications but which will have a cycle-life and abrasion resistance many times greater than those of heater cords now in common use, and which comprises new materials cooperatively associated in a new relationship, to provide a heater cord which may be built into an appliance and function as a permanent part thereof throughout its lifetime.

For the purpose of illustrating the present invention, a superior heater cord of the HPD type, which is the type most commonly used, will be described, but it will be understood that the invention is not limited thereto but is applicable to the other types of heater cord mentioned above and to all electrical conductors in general where a long eX-life and high resistance to abrasion are requisite characteristics of the conductors. Referring to the drawings, the improved heater cord is indicated generally at I0 and comprises a pair of conductors Il each provided with a sepa- 3 rator I2, tubed insulation I3 and a covering of asbestos I4, the two asbestos-covered conductors being twisted together to form a single cord covered by a braid I5.

The conductors II constitute one of the novel features of the invention, contributing to the eX- traordinarily high-flex life of the superior cord, each conductor being made up of a, number of strands I6 of an alloy of cadmium and copper. The cadmium content of this alloy is from about 1% to about 1.5%, the alloy being designated by the American Society for Testing Materials in their publication A. S. T. M. Standards 1946, Part I-B, Nonferrous Metals, page 35, Note I as No. 85 graden-copper, cadmium. In its preferred embodiment, the cadmium copper strands I6, hereinafter referred to as cadmium copper alloy strands, are annealed so as to have a minimum stretch of about the annealing being done either before or after the strands are bunched. The size and number of strands I6 which go into a single conductor II depend in part upon such considerations as the conductivity of the strands and the over-all size of the finished cord. The conductivity of the cadmium copper alloy strands I6 is substantially 85% that of pure copper, but because of its greater ability to withstand high currents, no extra strands are used. Thus, for a standard cord designated by the American Wire Gauge (AWG) as No. 18, the number of cadmium copper alloy strands (of 0.005 inch diameter) is about 65. Other strand numbers for respective cord sizes are listed below.

No. of Strands (0.005 inch diameter) The size of the HPD heater cord used to illustrate the present invention is No. 17 and embodies about 82 cadmium copper alloy strands I6, each about 0.005 inch in diameter, the number of strands being substantially the same as would be used for similar size cord employing pure copper conductors. Although the aforesaid diameter of the strands is highly satisfactory from the standpoint both of the facility of manufacture and long flex-life, it will be understood that strands of other diameters may be used as, for example, strands as ne as 0.003 inch in diameter or as heavy as 0.0063 inch in diameter. In such instances, a corresponding increase and decrease respectively would be made in the number of strands for any given cord size.

The process most commonly used for forming each conductor II from a, plurality of individual strands I6 is known in the art as bunching and is carried out, in general, by threading all the strands together through a stationary die and over a pulley or capstan which is adapted to be rotated to twist the several strands together.

It will be understood, however, that other techniques may be used to form the conductors as, for example, the processes of concentric stranding or rope stranding, each of which is well known in Jme art.

However, the preferred method of forming each conductor from the individual strands is by bunching. The lay or distance between successive twists of the bunched strands may vary from one-half inch to two inches in length and is preferably substantially three-quarters of an inch and in a right-hand direction, as indicated in Fig. 1.

Each conductor I I is provided with a serving of cotton yarn I2 wound around the conductor with a length of lay no shorter than the lay of the conductor strands and preferably in the same direction. In forming this cotton serving, which is hereinafter referred to as a separatorf a plurality of ends II of a cotton yarn as, for example, twelve ends of a No. 10 two ply soft natural cotton, are wound around each conductor I I with a substantially three-quarter-inch length of lay and in a right-hand direction corresponding to the direction of twist of the cadmium copper alloy strands I6. Although other size yarns may be used, a relatively-large size of yarn is preferred, since it has been found to contribute signicantly to better life-cycle in the finished heater cord. The present invention features the discovery that a cotton-yarn serving used in combination with a conductor consisting of a plurality of annealed cadmium copper alloy strands having the thermoplastic insulation material applied thereto as hereinafter described, contributes directly to the unexpectedly high flex-life of the heater cord and to its increased tensile strength.

Following the application of the cotton yarn I2 to the conductors I I, each is adapted to be coated with a plastic coating of insulation I3 by any of the methods of thermo-tubing known in the art. Formerly rubber or rubber-like materials such, for example, as cured or uncured compounds of Buna S have been used almost universally as a dielectric. The present invention features the discovery of an improved dielectric or insulation material which, in conjunction with the cadmium copper alloy conductors and cotton serving, effects an unexpectedly high cycle-life for the heater cord. The superior insulation of this invention comprises a polymerized vinyl-resin compound containing polyvinyl chloride or one containing a copolymer of vinylchloride or both. In addition to the thermoplastic resin, the compounds of these resins contain suitable plasticizers, stabilizers, and possibly pigments and llers. One typical Vinylite compound found to be satisfactory is known as VE5901 the composition of which is as follows:

and vinylacetate (CH=CH2 o o o CH3 Percent Vinylite VYNW 63.8 Dioctyl phthalate 20.4 Tricresyl phosphate 8.7 Sohio oil 1.0 Basic lead carbonate 3.8 Fused lead stearate 0.3

Litharge 2.0

In this connection, it should be pointed out that insulation materials which contain traces of sulphur as, for example, cured or uncured rubber and compounds of Buna S are admittedly harmful to copper conductors or conductors containing copper due to the afiinity of copper for sulphur. Heretofore, cotton servings have been used for the purpose of separating rubber and rubber-like insulation materials from the copper conductor so as to minimize the deleterious effects of the sulphur on the copper, but despite this precaution the sulphur is present as a potential enemy of the copper and will ultimately seriously affect the life of the conductor. The polymerized vinyl-resin compounds disclosed herein and used as insulation material for the conductors do not attack either the copper or cadmium constituents of the conductors nor the alloy or alloys thereof and consequently may be coated directly onto the bare conductors Without having any harmful effect thereon, the use of the separator in the improved heater cord of this invention being primarily for the purpose of increasing the flex-life and tensile strength of the conductors. As used on the separator wound conductors of the improved heater cord, the Vinylite insulation I3 has a wall thickness of about 0.020 inch but may vary from about 0.0156 inch to about 0.0312 inch.

The insulated conductors are adapted to be provided with a covering of a heat insulation material such as asbestos fibers which may be and preferably is in the form of roving I4 wound around each insulated conductor and constituting the ller of the completed cord. It will be understood, however, that the asbestos bers may be applied in other Ways as, for example, by carding or blowing techniques well known in the art. Where asbestos rovings are used as fillers, a plurality of ends, preferably seven, are Wound about each conductor with a substantially twoand-a-half-inch right-hand length of lay, the quality of the asbestos being preferably a sevencut Underwriters Grade containing a maximum of substantially admixed cotton and rayon. The minimum weight of asbestos roving which is used for each thousand feet of Wire is specified by the Underwriters Laboratory and in general is not greatly exceeded. The table below lists the minimum weights of asbestos roving per thousand feet of cord for heater cords of various sizes.

Minimum Weight of Asbestos per 1,000 Ft.

AWG Size Two of the roving-covered conductors are then twisted together to form a single cord. In the preferred construction of a heater cord of the HPD type, the conductors are twisted together in a left-hand direction, the length of lay being substantally 2 inches.

The two twisted conductors are adapted to be held together by a tubular covering or sheath I5 which, in the embodiment shown, comprises a braid, although a rubber or equivalent type of sheath may be used. Heretofore, braids have comprised cotton or rayon strands, but these materials have very little abrasion resistance and are readily inflammable. Moreover, eiorts to improve the abrasion resistance and the flex-life of the cord by using heavier strands, has resulted in a relatively-heavy unwieldly cord of large diameter. In carrying out the present invention, it has been discovered that a braid comprising monofilaments of a polyamide formed by the polymerization of the nylon salt hexamethylenediammonium-adipate and commonly known as nylon resin, had superior abrasion resistance, was substantially non-smoldering and, in cooperation with the cadmium copper alloy strands, contributed to the exceptionally-high cycle-life of the heater cord. The monolaments of the nylon resin may vary in diameter from about 0.003 inch to about 0.015 inch and are preferably about 0.007 inch in diameter, five ends of the nylon monolaments being braided on a conventional braiding machine such as, for example, a 24- carrier Wardwell braider. For optimum results, it is desirable to use Slip-wires to form a relatively loose braid on the twisted conductors and to provide a basket type of weave.

An HPD type of heater cord constructed as described above, has been found to have a tremendously greater flex-life than has characterized any other heater cord of its type, as a consequence of which the superior cords may be built into appliances as a permanent part thereof with the justifiable expectation that the cord will stand up throughout the life of the appliance. Moreover, the cord is substantially non-smoldering, will not Wick up liquids, has a high resistance to abrasion and presents a pleasing' appearance.

The invention may be carried out in other specie ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

I claim:

1. An improved heater cord comprising a plurality of conductors, each consisting of an annealed alloy of cadmium and copper wherein the cadmium content is from about 1% to about 1.5%; a separator wound on each conductor; a polymerized vinyl-resin dielectric material coated on each conductor, said polymerized vinylresin dielectric comprising a copolymer of vinylchloride and vinylacetate; a heat-insulation material covering each of said dielectric-coated conductors; and a sheath enclosing the heat-insulated delectric-coated conductors.

2. An improved heater cord comprising a plurality of conductors, each consisting of an annealed alloy of cadmium and copper wherein the cadmium content is from about 1% to about 1.5%; a separator wound on each conductor; a polymerized vinyl-resin dielectric material coated on each conductor, said polymerized vinyl-resin dielectric comprising a copolymer of vinylchloride and vinylacetate; a heat-insulation material covering each of said dielectric-coated conductors; and a braid enclosing the said dielectric-coated conductor, said braid comprising filaments of a polyamide resin.

3. An improved heater cord comprising a plurality of conductors, each consisting of an annealed alloy of cadmium and copper wherein the cadmium content is from about 1% to about 1.5%; a separator wound on each conductor; a dielectric comprising a copolymer of vinylchloride-and-vinylacetate-resin compound coatstrands of each conductor the said Vinylite compound VE5901 having the following composition: Vinylite VYNW (Vinyl chloride 96 to 97%) Percent (Vinyl acetate 3 to 4%) 63.8 Dioctyl phthalate 20.4 Tricresyl phosphate 8.7 Schio oil 1.0 Basic lead carbonate 3.8 Fused lead stearate 0.3 Litharge 2.0

asbestos roving wound around each dielectriccoated conductor, the said pair of roving-wound dielectric-coated conductors being twisted t0- gether in a direction opposite to the direction of twist of said conductor strands to form a. Single cord; and a braid comprising monolaments of nylon enclosing said single cord.

JOSEPH B. WHYLAND.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,864,512 Abbott June 28, 1932 1,891,495 Bassett et al Dec. 20, 1932 1,989,483 Lewis Jan. 29, 1935 2,313,234 Gavitt Mar. 9, 1943 2,337,428 Tietz Dec. 21, 1943 OTHERl REFERENCES An article, Flameproof Wire and Cable Vital to Safety at Sea, found in Bakelite Review, vol. 16, No. l, for April 1944; pages 4 through 6; a copy of article in Div. 65.

A table in the book, Engineering Alloys, by

vWoldman and Metzler, Revised Ed. 1945; page 539; serial number of alloy 12,061; a copy of book in Div. 3. 

